Method of rolling and treating silicon steel



Patented Apr. 5, 1938 umrrn sures PAT NT OFFICE turmoil or -Hanau-on-the-Main company No Drawing. Application Germany No. 88,683. In

4 Claims. (01. 148-12) 5 This invention relates to metallurgy and more particularly to the art of mechanically deforming silicon steel into sheet, strip and the like materials suitable for uses such as transformer'cores.

5 or the magnetic parts of electrical equipment 'wherein high initial and maximum permeability and low watt loss are sought. Silicon steel heretofore found useful for such purposes comprises a low carbon iron containing from about 3.0%

m to about 5.0% silicon with or without accompanying amounts of aluminum or manganese or both approximating some few tenths of a per cent and this invention' is applicable to all such compositions.

For use as transformer cores the final fabricated sheet or strip material, which usually is of a thickness approximating'.35 mm. (.014 inch),

' should possess the maximum permeability and minimum watt loss characteristics possible. I have discovered that an extraordinarily high permeability and relatively low wattloss may be imparted to such steels by the practice of the combination of steps described in the paragraphs below. In particular, while others have employed one or more intermediate annealing steps between successive cold-rolling operations, I have secured equal or superior properties by omitting such annecessarily at about room temperatures, until the desired final thickness, e. g. .35 mm.- (.014 inch) is obtained. I then subject the material to an annealing at temperatures approximating 1250 C. in a non-oxidizing and non-carburizing (with respect to the silicon steel) atmosphere (preferably hydrogen) following which the material is cooled. This final annealing of the cold worked metal at temperatures approximating 1250-C.' may be varied widely as to time interval without departure from the present invention, depending in part upon the degree of cold working imparted and in part-upon. the degree of metal purification obtained thereby. The time interval must be at least sumcient to attain substantially uniform temperatures throughout the metal and may be,

some AND mama srucox STEEL m mammalian-mama.

assignor to Heraens-Vac Germany, lle A. G.,

. Gelnna July 2, 1930; Serial 0mmza, 1935 as long as 3 to 12 hours. Preferably the cooling is relatively slow or retarded to suchan extent as to prevent the introduction of cooling stresses and strainsin the metal, f. i. '1 hours from 1250 to 300 C.

During the hot working of this steel I preferably maintain the material at a temperature ap proximating 1100 C. until the material approximates 5 mm. (.20 inch) in thickness or some other thickness between 8 to 20 times the desired final thickness and then lower the rolling temperature to approximately 850 0., heating the material if required between passes through the rolls until the thickness of the. material approximates 5 to 8' times the desired final thickness which in thecase of .35 mm. (.014 inch) material may be, for example, 2 mm. (.08 inch).

Following the annealing and rapid cooling step of my invention, I may mechanically deform the material at about atmospheric temperatures down to the desired final size, or I may deform initiallyat a cold'working temperature above atmospheric temperatures or at gradually falling cold working temperatures, the final deformation however, or

the last few passes through the rolls being -atabout atmospheric temperatures, the precise mode of cold working depending primarily upon the total reduction of thickness to be accomplished after hot rolling by the cold rolling step. When hot working proceeds to-the minimum thickness (approximately 5 times the desired final thickness) I may cold work at atmospheric temperatures down to the desired final size without difficulty. when, however, hot working is terminated at 8 times the desired final thickness I find that it is sometimes preferable to initiate cold rolling at temperatures approximating 450 0 and to continue rolling at this temperature or at graduthe material at least approximates 5 times the desired final thickness whereupon rolling at atm'ospheric temperatures can be initiated, if desired.

As a specific example of the practice of the present invention a low carbon silicon iron alloy containing 3.5 per cent silicon and .15 per cent manganese when rolled to a final size of .35 mm.

(.014 inch), as above described, produces sheet material having an initial permeabilityof about 1,000 to 1,900, a maximum permeability of 35,500

and a watt loss of .56 watt per kilogram at a flux density of 10,000 gausses at 50 cycles.

A similar sheet similarly manufactured from a low carbon iron alloy containing 3.5 per cent silicon, 0.10 per cent manganese and 0.10 per cent ally lowering temperatures until the thickness of i 9. watt loss of .57 watt per kilogram at the aluminum showed an initial permeability of 900 to 1,700, a maximum permeability of 35,300 and same flux density and at 50 cycles.

These results indicate that by the practice 01- the present invention an extraordinarily high permeability and low watt loss material may be obtained.

Having broadly and specifically described the and several 'modifications" thereof, it is apparent that many modifications present invention and adaptations thereof may be made without departing essentially therefrom, and all such modifications and adaptations are contemplated as fall within the scope of the following claims:-

What I claim is: 1. In the rolling and treatingof silicon steel for the manufacture of transformercore or other in a substantially non-oxiding and non-carburizing atmosphere and then slowly cooling the material to atmospheric temperatures in the said atmosphere.

2. The method of rolling and treating silicon steel for the manufacture of material suitable for use as transformer cores, which comprises rolling the said steel at a hot working temperature approximating 1100 C. to a thickness be.- tween 8 and 20 times the desired final thickness, continuing the rolling at a hot working temperature approximating 850 .C. to a thickness between 5 and 8 times the desired final thickness, annealing the hot worked material at a temperature approximating 1000 C. for a time interval approximating one hour, rapidly cooling the an-' nealed material to atmospheric temperaturm,

\ rolling the quenched material at a cold working temperature down to the desired final thickness 1250 materlal to atmospheric temperatures.

steel transformer the desired final thickness,

final thic tures, heat-treating. the final rolled product inv a substantially non-oxidizing and non-carbm-iztemperatures appr ximating C.,- and slowly cooling the heat-treated ing atmosphere at 3. The method of rolling and treating silicon material to obtain relatively high permeability and relatively low watt loss characteristics which comprises hot rolling the steel at temperatures approximating 1100 C. to a thickness somewhat thicker than 5 to 8 times continuing hot rolling at temperatures approximating 850 0. down toathicknesswithintherange5to8timesthe desired final thickness, heating the hot rolled material to'a temperature approximating 1000' C. for a time interval of about an hour to anneal the same, rapidly quenching the annealed material, cold rolling the material to the desired the final few-passes at. least being at'temperatures approximating atmospheric temperatm'esheat -treating the cold rolled material at temperatures approximating 1250 C. in a substantially non-oxidizing. and nbn-carburizlng atmosphereand slowly cooling the material to at mospheric temperatures.

4. The method of rolling and treating silicon steel into sheet, strips and the like suitable for use as transformer core material which comprises rolling the steel at temperatures of about 1100. 0. down to a thickness of about .10 to 15 times the desired final thickness, continuing hot rolling at temperatures of about 850 0. down to a thickness of about 5 to 8 times the desired final thickness, annealing the hot rolled material at a temperature of about 1000 C. for a time interval of about an hour, rapidly quenching the annealed material, rolling the material at a temperature of about 450 C. to a thickness nearly that of the desired final thickness, rolling to the desired final thickness at temperatures approximating atmospheric' temperatures, heat-treating the material in a substantially non-oxidizing and non-carburizing atmosphere for a time interval of up to about 3 hours and at a temperature of about 1250' C. and then slowly cooling the heat-treated material to atmospheric" temperatures.

HANS 

